NEW YORK (Reuters Health) - Coinfection with hepatitis B virus (HBV) and hepatitis C virus (HCV) is associated with substantially higher risk of hepatocellular carcinoma than single infections, but the complex interactions of the viruses vary depending on gender and age, a study from Taiwan shows.

The researchers report that in general, coinfection produced weaker effects than previously reported.

"By the age of 75 years, one quarter of patients or more affected by chronic viral hepatitis will be affected by hepatocellular carcinoma," or HCC, the research team noted in an August 22nd online paper in the Journal of Clinical Oncology.

Led by Dr. Yen-Tsung Huang of Harvard University, the study tracked 23,820 residents of Taiwan aged 30 to 65 years at enrollment in 1991-1992.

Overall, 17.44% were seropositive for HBV surface antigen and 5.52% were seropositive for antibodies against HCV.

Altogether, 477 subjects developed HCC.

The cumulative lifetime incidence of HCC for was 38.35% for men with both viruses and 27.40% for women with both viruses.

Men and women who were seropositive only for HBsAg had cumulative lifetime HCC rates of 27.38% and 7.99%, respectively. These rates in men and women with only HCV were 23.73% and 16.71%, respectively.

In contrast, the cumulative lifetime incidence rates for subjects with neither virus were 1.55% in men and 1.03% in women.

On multivariate analysis, the hazard ratio for HCC was 19.5 for those positive for both infections.

The interactive effects of the two viruses varied based on age, however. The HCC risk with dual infection was "sub-additive" before the age of 65 years, especially in men. But after age 65, the risk with dual infection was "consistently higher than that for single infection."

Specifically, in older patients, the HR in men was 22.38 for dual infection vs. 8.94 and 12.34 for single infections with HBV and HCV, respectively. In women after age 65, HRs for HCC were 27.29 with dual infection, 6.58 with HBV and 15.01 with HCV.

"With the increase in age, the HCC risk decreased in HBsAg-seropositive men but increased in anti-HCV-seropositive women," said study senior author Dr. Chien-Jen Chen, of the National Taiwan University in Taipei, in an email to Reuters Health.

The authors advise more intensive clinical management of patients with dual infection.

"The therapy of chronic HBV/HCV infection using antivirals and/or interferon may reduce the risk of newly developed HCC," Dr. Chen said. "Frequent liver surveillance using various imaging methods (ultrasonography, CT scan, angiogram, etc.) may help early detection of small HCC, which may be treated more effectively and efficiently by surgery or embolization. The HCC case fatality may thus be lowered."